Sleep paralysis is a condition characterized by brief periods of paralysis as the patient falls to sleep or wakes up. It is usually associated with other sleep disorders, rather than appearing on its own, and since it is often accompanied by hallucinations, sleep paralysis can sometimes be very frightening for patients. People often feel what they describe as a presence in the room when they experience a bout of sleep paralysis, and many cultures have complex folklore surrounding this sleep disorder.

This condition is especially common in people who experience narcolepsy, but it is also associated with lack of sleep, poor sleeping conditions, stress, and other sleep disorders. On its own, sleep paralysis is not inherently harmful, although it can be scary, and it can also be a sign of a more serious problem which needs to be addressed. Repeated episodes of sleep paralysis, especially if accompanied by terrifying hallucinations, are definitely cause for a trip to the doctor.

When someone experiences sleep paralysis, the body feels heavy and immovable, and the patient may feel like he or she cannot speak. The condition is actually very similar to REM atonia, a natural form of paralysis which sets in during the deep stages of REM sleep to keep the body from acting out the movements experienced in dreams. Sleep paralysis, however, occurs at the edges of REM sleep, rather than in the most intense part.

Sleep paralysis episodes can last a few seconds to several minutes. Sometimes, external stimuli such as a voice or touch can pull someone out of sleep paralysis, and in other cases, the patient may be unreachable. Sleep paralysis occurs most often when people sleep on their backs, and in some cultures it is known as the “Old Hag,” in reference to the idea that it is caused by an old hag sitting on the patient's chest.

Some people have suggested that sleep paralysis might be the rational explanation behind myths of alien abductions, succubi, vampires, and other malevolent nighttime visitors. Since the hallucinations associated with this sleep disorder can be extremely vivid and often very strange, people with active imaginations might have had trouble understanding that the events “experienced” during sleep paralysis did not actually happen.

Sometimes, sleep paralysis can be addressed with the use of prescription drugs. However, it can also be beneficial to make adjustments to a sleep routine, and to probe into the root causes of the sleep paralysis to see if those can be treated to eliminate the issue. Other people take a different approach, using psychology in an attempt to control the hallucinations, turning the sleep paralysis into an interesting, rather than frightening, experience.